Smokeless propellent compositions containing polyester resin

ABSTRACT

1. Method for producing thrust in the absence of smoke, said method comprising burning a propellant composition consisting essentially of a cured intimate mixture of a solid nonmetallic, inorganic oxidizing salt in amount from about 45 to about 90 percent by weight of the total propellant composition, a combustible organic resin, a catalytically effective quantity of a burning rate acceleration catalyst selected from the group consisting of the nitrate salts of zinc, lithium, iron, chromium, and mixtures thereof so as to produce nonsmoking gases, and exhausting said gases through an orifice to produce thrust.

United States Patent Batchelder et al.

[451 Apr. 4, 1972 [72] Inventors: George W. Batchelder, Yucaipa; Gilbert A. Zimmerman, Monrovia, both of Calif.

[73] Assignee: Aerojet-General Corporation, Azusa,

Calif.

[22] Filed: June 12,1956

21 App1.No.: 590,998

[52] U.S.Cl ..149/19, 149/20 [51] Int. Cl. 1 ..C06d 5/06 [58] Field ofSearch ..52/0.5,l4;60/35.4;149/19, 149/20, 61

[56] References Cited UNITED STATES PATENTS 2,159,234 5/1939 Taylor ..149/19 2,622,277 12/1952 Bonell et a1.. ....l49/19 2,783,138 2/1957 Parsons ....149/19 2,926,613 3/1960 Fox ....149/19 2,931,437 4/1960 Smith ..149/19 1,506,322 8/1924 ONeill ..110/1 2,637,274 5/1953 Taylor et a1 ..52/0.5 X

2,740,702 4/1956 Mace ..52/O.5

2,771,035 11/1956 Clark ..52/0.5 X

OTHER PUBLICATIONS Zaehringer Solid Propellant Rockets," American Rocket Co., Box 1112, Wyandotte, Mich. 1955, p. 50

Primary Examiner-Benjamin R. Padgett Att0rneyD. Gordon Angus, Edward G. Ansell and T. Reid Anderson EXEMPLARY CLAIM 1. Method for producing thrust in the absence of smoke, said method comprising burning a propellant composition consisting essentially of a cured intimate mixture of a solid nonmetallic, inorganic oxidizing salt in amount from about 45 to about 90 percent by weight of the total propellant composition, a combustible organic resin, a catalytically effective quantity of a burning rate acceleration catalyst selected from the group consisting of the nitrate salts of zinc, lithium, iron, chromium, and mixtures thereof so as to produce nonsmoking gases, and exhausting said gases through an orifice to produce thrust.

17 Claims, No Drawings SMOKIELESS PROPELLENT COMPOSITIONS CONTAINING POLYESTER RESIN This invention relates to new burning rate acceleration catalysts for solid propellant compositions.

Solid, non-metallic propellant compositions are used for rocket and ordnance projection, as well as for assisted aircraft take-offs. Such propellant compositions are composed essentially of two main components; namely, a combustible organic resin fuel and an oxidizing material.

The fuel component of the propellant needs only to be combustible and possess physical properties which permit it to be cast or molded into a propellant grain. A wide variety of resins, such as asphalt, polyesters, polyalcohols, polynitroalkenes, and mixtures thereof, are known to be useful fuels.

The oxidizing material is usually an inorganic oxidizing salt.

*Metal salts, such as potassium perchlorate, are commonly used; however, upon combustion they form solid particles which create large quantities of undesirable smoke. Smoke is highly undesirable for military purposes of concealment, moreover, such metallic salts are considerably more expensive than ammonium salts. Hence, nonmetallic inorganic oxidizing salts such as hydrazine and ammonium salts are preferred, for upon combustion they produce no visible products. Ammonium salts are ordinarily employed due to their cost and availability.

The desirability of rapid burning propellants for rocket and ordnance projections is well established. Metal-containing oxidizers generally provide fast burning compositions. Unfortunately, propellants utilizing inexpensive, nonmetallic, inorganic, oxidizing salts as the oxidizer have heretofore exhibited only relatively slow burning rates. For example, ammonium nitrate oxidized propellants have never been known to burn at rates in excess of 0.10 in./sec., even though burned in the presence of burning rate acceleration catalysts such as ammonium dichromate.

We have now found that by incorporating nitrate salts of metals such as lithium, iron, chromium and zinc into propellants utilizing nonmetallic, inorganic oxidizing salts as oxidizers, that the burning rate of said propellants is increased as much as 100 percent. The metal salts are present in the compositions in such small amounts, usually from about 0.05 to about 5 percent by weight of the composition, that the smoke formed by their combustion is negligible. The catalysts of this invention are particularly valuable when employed in combination with conventional burning rate acceleration catalysts such as ammonium dichromate; however, their use is not limited to this particular embodiment of the invention.

Oxidizers useful in the practice of this invention are nonmetallic chlorate, perchlorate, and nitrate salts such as ammonium nitrate, ammonium chlorate, ammonium perchlorate and hydrazine nitrate. The nonmetallic nitrate salts are preferred due to their availability, stability and the ease with which they can be handled. The nitrate salts, however, usually do not burn as rapidly as the chlorate or perchlorate salts.

The oxidizer, in a finely divided condition, is dispersed throughout the fuel component of the propellant. Ordinarily, the oxidizer is present in an amount of from about 45 to about 90 percent by weight of the total composition. Optimum results are obtained when there is sufficient oxygen in the propellant to oxidize all of the carbon in the fuel to carbon monoxide and one-third of the hydrogen to water.

Combustible organic resinous fuels useful in propellant compositions of this invention are: asphalt, polymers and copolymers of alkenes, arylalkenes, alkynes, alkenyl diglycols, allyl alkenoates, alkenyl alkanoates, alkenoamides, and amidoalkenyls, and unsaturated alkyd resins heteropolymerized with the above compounds.

Asphalts having softening points of about 180 F. to about 220 F., and penetration values of about 7 to 9 mm./5 sec./ 100 g. at a temperature of 720 F., are usually preferred for rocket fuel due to their ballistic properties. When castability and low expansion coefficients are not essential, other grades of asphalt can be used. To improve the physical properties of the asphalt, a condensation product of sebacic acid and a polyhydric alcohol, a wax such as cetyl acetamide, or a hydrocarbon oil is often incorporated into the asphalt. Suitable fuels of this type are more fully disclosed in assignees copending application Ser. No. 634,609, filed Dec. 12, 1945, and assignees US Pat. No. 2,565,265, issued Aug. 7, 1951.

A typical formulation of an asphalt base propellant composition is as follows:

Propellant Composition A Asphalt 10%7: Cetyl acetamide 3% Castor oil 8% Dibutyl sebacate Il /2% Ammonium perchlorate 75% Propellant Composition B N,N-dimethyl acrylamide 22.94

Ammonium nitrate 76.81 Methyl amyl ketone eroxide 0.25

(Polymerization catalyst) Total: l00.00

The polyamide propellant grain can be prepared by mixing the amide, oxidizer and polymerization catalyst until a homogeneous mixture is obtained and curing the mixture at a temperature of from about 25 C. to about C.

Polyalkenes useful as fuels are: polyisobutylene, butadienestyrene copolymers, butadiene-acrylonitrile copolymers, and isobutylene-isoprene copolymers. Suitable fuels of this type are more fully disclosed in assignees copending application Ser. No. 637,004, filed Dec. 22, 1945.

A typical formulation of a propellant composition having a polyolefinic fuel component is as follows:

Propellant Composition C Ammonium perchlorate 76.00 Copolymer: 24.00

lsobutylene 98.5% lsoprene 1.5%

Total: 100.00

The polyolefin-base propellant grain can be prepared by roll milling the oxidizer into the polyolefin until a homogeneous mixture is obtained and then pressing the material into sheets or discs.

Polyalkenoates useful as fuels are: polymers and copolymers of acrylic acid, acrylic acid esters, methacrylic acid and methacrylic acid esters. Suitable fuels of this type are more fully disclosed in assignees copending application Ser. No. 321,943, filed Nov. 21, 1952. A typical formulation of a propellant composition having a polyester fuel component is as follows:

Propellant Composition D Hydrazine nitrate 60.00% Methyl acrylate 25.60% Allyl diglycol carbonate 3.56% Methyl methacrylate 0.40% t-butyl peroxide (polymerization 0.80%

catalyst) The polyester-base propellant grain is prepared by mixing the various monomers, oxidizer and polymerization catalyst until a homogeneous mixture is obtained, and then curing the mixture in a mold.

Alkyd resin fuels are usually polyesters prepared by the condensation of a polycarboxylic acid with a polyhydric alcohol, one or both of which contain olefinic linkages. Among the unsaturated polycarboxylic acids which are ordinarily used in the.

preparation of such polyesters are maleic, fumaric, citraconic, mesaconic, itaconic acids, etc. Saturated acids found to be useful are such acids as oxalic, malonic, succinic, and glutaric, etc. The polyhydric alcohols useful are dihydric alcohols such as ethylene glycol, propylene glycol, glycol, etc.; as well as trihydric alcohols such as glycerol; tetrahydric alcohols such as the erythritols; pentahydric alcohols such as arabitol, etc.; or mixtures of any of these alcohols.

The olefinic component of the fuel can be, for example, styrene, vinyl acetate, acrylic acid esters, methacrylic acid esters, allyl compounds such as allyl diglycol carbonate, diallyl maleate, diallyl glycollate, and other olefinic components such as propylene and butadiene, as well as the acetylenes. In general, any unsaturated compound compatible with the resin, and which will polymerize with it, is suitable; this includes all unsubstituted olefins and, in addition, many substituted olefins. Suitable fuels of this type are more fully disclosed in assignees copending application Ser. No. 109,409, filed Aug. 9, 1949.

A typical formulation of a propellant composition utilizing an alkyd resin fuel is as follows:

Propellant Composition E Ammonium dichromate 1.99

Ammonium nitrate 72.79

Polyester, by wt. 92 9.79

43.00% Diethylene glycol 44.25% Adipic acid l.7$% Maleic anhydride Styrene 2.66 Methyl acrylate 12.22 Polymerization catalyst and lecithin 0.49

Total: 100.00

The alkyd resin-base propellant grains are prepared by blending together the polyester and olefinic components of the fuel, the oxidizer and the burning rate acceleration catalyst. If desired, a polymerization catalyst can also be added. This mixture is cast into a mold and the fuel allowed to heteropolymerize at a temperature in the range of from about C. to about 100 C., and preferably at a temperature below 60 C.

The polymerization catalysts usually employed in such propellant compositions are organic peroxides such as benzoyl peroxide, lauryl peroxide, acetobenzoyl peroxide, ditertiary butyl peroxide, methyl ethyl ketone peroxide, l-hydroxycyclohexyl hydroperoxide, cumene hydroperoxide, and cycloalkane hydrocarbon peroxide, and peresters such as tertiary butyl perbenzoate and diperphthalate.

Various other ingredients can also be added for specific purposes without departing from the scope of the invention. For example, lecithin can be added to improve the castability of the uncured propellant. t-Butyl catechol or cobalt 2-ethyl hexanoate is often added as a polymerization modifier.

The propellant grains prepared in the above described manner can withstand rough handling and will perform satisfactorily at temperatures in the range of from about 65 F. to about 165 F.

The particular fuel employed in the propellant composition does not affect the function of the burning rate acceleration catalysts of this invention. In addition to the propellant compositions described above, these catalysts can be used in compositions utilizing fuel components such as polymers of nitroalkenes, nitroalkynes, nitro-containing acids and their esters, as well as other combustible organic polymeric materials.

The burning rate acceleration catalysts herein described are usually incorporated into the propellant compositions in finely divided form and are mixed with the fuel usually at the same time the oxidizer is mixed. To illustrate the improvement in the burning rate brought about by incorporating these catalysts into a solid propellant, the results of a series of burning tests are shown in Table I. These tests were made using propellant E, described above. In the absence of a catalyst, propellant E does not readily sustain combustion, therefore, as

a matter of convenience in establishing a burning rate standard for comparative purposes, ammonium dichromate was incorporated in all of the sample grains. It is to be understood that these examples are presented merely as a means of illustration and are not intended to limit the scope of the invention in any way.

TABLE I of burning rate Acceleration Catalyst present Acceleration Catalyst Burning Rate As can be seen from the data presented in Table I, a substantial increase in the burning rate of the propellant was effected by the catalysts of this invention. Increases in burning rate of the magnitude herein obtained are particularly valuable in rocketry and ordnance projection, for such projectiles are ordinarily guided only during the period of their launching. When the full thrust created by the propellant is available during this time, the projectile can be more effectively directed.

Due to the great increase in the burning rates of non-metallic, smokeless propellant compositions induced by the above catalysts, and their applicability to propellants having a wide variety of fuel components, it is apparent that these catalysts will find extended and valuable use in the field of rocketry and ordnance propulsion.

We claim:

1. Method for producing thrust in the absence of smoke, said method comprising burning a propellant composition consisting essentially of a cured intimate mixture of a solid nonmetallic, inorganic oxidizing salt in amount from about 45 to about percent by weight of the total propellant composition, a combustible organic resin, a catalytically effective quantity of a burning rate acceleration catalyst selected from the group consisting of the nitrate salts of zinc, lithium, iron, chromium, and mixtures thereof so as to produce nonsmoking gases, and exhausting said gases through an orifice to produce thrust.

2. A solid, smokeless, propellant composition consisting essentially of a cured intimate mixture of a solid, nonmetallic,

inorganic, oxidizing salt, in an amount of from about 45 to about 90 percent by weight of the total propellant composition, a combustible organic resin, selected from the group consisting of:

a. asphalt;

b. olefinic polymers;

c. alkyl alkenoate heteropolymerized with olefins;

d. unsaturated polyester resin consisting of the condensation product of saturated polyhydric alcohol and polycarboxylic acid heteropolymerized with an unsaturated compound; and

e. alkenoamide polymers; and from about 0.05 to about 5.0 percent by weight of a burning rate acceleration catalyst selected from the group consisting of the nitrate salts of zinc, lithium, iron, chromium and mixtures thereof.

3. The composition of claim 2 wherein the combustible, or-

ganic resin is asphalt.

'4. The composition'of claim 2 wherein the combustible, organic resin is an olefinic polymer.

5. The composition of claim 2 wherein the combustible, organic resin is alkyl alkenoate heteropolymerized with an olefin.

6. The composition of claim 2 wherein the combustible, organic resin is an unsaturated polyester resin consisting of the condensation product of a saturated polyhydric alcohol and polycarboxylic acid heteropolymerized with an unsaturated compound selected from the group consisting of lower alkenes, lower alkynes, phenyl substituted lower alkenes, lower alkyl dienes, lower alkenyl esters of lower alkanoic acids, lower alkyl esters of alkenoic acids, lower alkenyl esters of lower alkenoic acids, allyl diglycol carbonate, diallyl diglycollate, lower alkenoamide and mixtures thereof; and a burning rate acceleration catalyst selected from the group consisting of the nitrate salts of zinc, lithium, iron, chromium and mixtures thereof.

7. The composition of claim 2 wherein the combustible, organic resin is an alkenoamide polymer.

8. The composition of claim 2 wherein the nonmetallic, inorganic, oxidizing salt is selected from the group consisting of nitrate, perchlorate, and chlorate salts of ammonia and hydrazine.

9. A solid, smokeless, propellant composition consisting of a cured intimate mixture of from about 45 to about 90 percent by weight a solid, inorganic, nonmetallic, oxidizing salt; from about 55 to about percent by weight of a polyester resin consisting of the condensation product of an unsaturated polyester resin consisting of the condensation product of a saturated polyhydric alcohol and polycarboxylic acid heteropolymerized with a lower alkyl alkenoate; and from about 0.05 to about 5 .0 percent by weight of the total propellant composition of a burning rate acceleration catalyst selected from the group consisting of the nitrate salts of zinc, lithium, iron, chromium and mixtures thereof.

10. The composition of claim 9 wherein the burning rate acceleration catalyst is present in an amount of from about 0.05 to about 5.0 percent by weight of the total propellant composition.

1 1. A solid, smokeless, propellant composition consisting of a cured intimate mixture of from about 45 to about percent by weight of ammonium nitrate; from about 55 to about 10 percent by weight of a fuel component comprising an unsaturated polyester resin consisting of the condensation product of diethylene glycol, adipic acid, and maleic anhydride heteropolymerized with a mixture of styrene and methyl acrylate; and from about 0.05 to about 5.0 percent by weight of the total propellant composition of a burning rate acceleration catalyst selected from the group consisting of the nitrate salts of zinc, lithium, iron, chromium and mixtures thereof.

12. A solid smokeless propellant composition consisting essentially of from about 45 to about 90 percent by weight of a solid inorganic oxidizing salt of ammonia; from about 55 to about 10 percent by weight of unsaturated polyester resin consistin of the condensation product of saturated polyh dric alcoho and polycarboxylic acid heteropolymerized wit an unsaturated compound; and from about 0.05 to about 5.0 percent by weight of the total propellant composition of chromium nitrate as a burning rate acceleration catalyst.

13. A solid smokeless propellant composition consisting essentially of from about 45 to about 90 percent by weight of a solid inorganic oxidizing salt of ammonia; from about 55 to about 10 percent by weight of unsaturated polyester resin consisting of the condensation product of saturated polyhydric alcohol and polycarboxylic acid heteropolymerized with an unsaturated compound; and from about 0.05 to about 5.0 percent by weight of the total propellant composition of ferric nitrate hydrate as a burning rate acceleration catalyst.

14. A solid smokeless propellant composition consisting essentially of from about 45 to about 90 percent by weight of a solid inorganic oxidizing salt of ammonia; from about 55 to about 10 percent by weight of an olefinic polymer; and from about 0.05 to about 5.0 percent by weight of the total propellant composition of chromium nitrate as a burning rate acceleration catalyst.

15. A solid smokeless propellant composition consisting essentially of from about 45 to about 90 percent by weight of a solid inorganic oxidizing salt of ammonia; from about 55 to about 10 percent by weight of an olefinic polymer; and from about 0.05 to about 5.0 percent by weight of the total propellant composition of ferric nitrate hydrate as a burning rate acceleration catalyst.

16. A solid smokeless propellant composition consisting essentially of from about 45 to about 90 percent by weight of a solid inorganic oxidizing salt of ammonia; from about 55 to about 10 percent by weight of asphalt; and from about 0.05 to about 5.0 percent by weight of the total propellant composition of chromium nitrate as a burning rate acceleration catalyst.

17. A solid smokeless propellant composition consisting essentially of from about 45 to about 90 percent by weight of a solid inorganic oxidizing salt of ammonia; from about 55 to about 10 percent by weight of asphalt; and from about 0.05 to about 5.0 percent by weight of the total propellant composition of chromium nitrate as a burning rate acceleration catalyst.

* IIK 

1. METHOD FOR PRODUCING THRUST IN THE ABSENCE OF SMOKE, SAID METHOD COMPRISING BURNING A PROPELLANT COMPOSITION CONSISTING ESSENTIALLY OF A CURED INTIMATE MIXTURE OF A SOLID NONMETALLIC, INORGANIC OXIDIZING SALT IN AMOUNT FROM ABOUT 45 TO ABOUT 90 PERCENT BY WEIGHT OF THE TOTAL PROPELLANT COMPOSITON, A COMBUSTIBLE ORGANIC RESIN, A CATALYTICALLY EFFECTIVE QUANTITY OF A BURNING RATE ACCELERATION CATALYST SELECTED FROM THE GROUP CONSISTING OF THE NITRATE SALTS OF ZINC, LITHIUM IRON, CHROMIUM, AND MIXTURES THEREOF SO AS TO PRODUCE NONSMOKING GASES, AND EXHAUSTING SAID GASES THROUGH AN OFFICE TO PRODUCE THRUST.
 2. A solid, smokeless, propellant composition consisting essentially of a cured intimate mixture of a solid, nonmetallic, inorganic, oxidizing salt, in an amount of from about 45 to about 90 percent by weight of the total propellant composition, a combustible organic resin, selected from the group consisting of: a. asphalt; b. olefinic polymers; c. alkyl alkenoate heteropolymerized with olefins; d. unsaturated polyester resin consisting of the condensation product of saturated polyhydric alcohol and polycarboxylic acid heteropolymerized with an unsaturated compound; and e. alkenoamide polymers; and from about 0.05 to about 5.0 percent by weight of a burning rate acceleration catalyst selected from the group consisting of the nitrate salts of zinc, lithium, iron, chromium and mixtures thereof.
 3. The composition of claim 2 wherein the combustible, organic resin is asphalt.
 4. The composition of claim 2 wherein the combustible, organic resin is an olefinic polymer.
 5. The composition of claim 2 wherein the combustible, organic resin is alkyl alkenoate heteropolymerized with an olefin.
 6. The composition of claim 2 wherein the combustible, organic resin is an unsaturated polyester resin consisting of the condensation product of a saturated polyhydric alcohol and polycarboxylic acid heteropolymerized with an unsaturated compound selected from the group consisting of lower alkenes, lower alkynes, phenyl substituted lower alkenes, lower alkyl dienes, lower alkenyl esters of lower alkanoic acids, lower alkyl esters of alkenoic acids, lower alkenyl esters of lower alkenoic acids, allyl diglycol carbonate, diallyl diglycollate, lower alkenoamide and mixtures thereof; and a burning rate acceleration catalyst selected from the group consisting of the nitrate salts of zinc, lithium, iron, chromium and mixtures thereof.
 7. The composition of claim 2 wherein the combustible, organic resin is an alkenoamide polymer.
 8. The composition of claim 2 wherein the nonmetallic, inorganic, oxidizing salt is selected from the group consisting of nitrate, perchlorate, and chlorate salts of ammonia and hydrazine.
 9. A solid, smokeless, propellant composition consisting of a cured intimate mixture of from about 45 to about 90 percent by weight a solid, inorganic, nonmetallic, oxidizing salt; from about 55 to about 10 percent by weight of a polyester resin consisting of the condensation product of an unsaturated polyester resin consisting of the condensation product of a saturated polyhydric alcohol and polycarboxylic acid heteropolymerized with a lower alkyl alkenoate; and from about 0.05 to about 5.0 percent by weight of the total propellant composition of a burning rate acceleration catalyst selected from the group consisting of the nitrate salts of zinc, lithium, iron, chromium and mixtures thereof.
 10. The composition of claim 9 wherein the burning rate acceleration catalyst is present in an amount of from about 0.05 to about 5.0 percent by weight of the total propellant composition.
 11. A solid, smokeless, propellant composition consisting of a cured intimate mixture of from about 45 to about 90 percent by weight of ammonium nitrate; from about 55 to about 10 percent by weight of a fuel component comprising an unsaturated polyester resin consisting of the condensation product of diethylene glycol, adipic acid, and maleic anhydride heteropolymerized with a mixture of styrene and methyl acrylate; and from about 0.05 to about 5.0 percent by weight of the total propellant composition of a burning rate acceleration catalyst selected from the group consiSting of the nitrate salts of zinc, lithium, iron, chromium and mixtures thereof.
 12. A solid smokeless propellant composition consisting essentially of from about 45 to about 90 percent by weight of a solid inorganic oxidizing salt of ammonia; from about 55 to about 10 percent by weight of unsaturated polyester resin consisting of the condensation product of saturated polyhydric alcohol and polycarboxylic acid heteropolymerized with an unsaturated compound; and from about 0.05 to about 5.0 percent by weight of the total propellant composition of chromium nitrate as a burning rate acceleration catalyst.
 13. A solid smokeless propellant composition consisting essentially of from about 45 to about 90 percent by weight of a solid inorganic oxidizing salt of ammonia; from about 55 to about 10 percent by weight of unsaturated polyester resin consisting of the condensation product of saturated polyhydric alcohol and polycarboxylic acid heteropolymerized with an unsaturated compound; and from about 0.05 to about 5.0 percent by weight of the total propellant composition of ferric nitrate hydrate as a burning rate acceleration catalyst.
 14. A solid smokeless propellant composition consisting essentially of from about 45 to about 90 percent by weight of a solid inorganic oxidizing salt of ammonia; from about 55 to about 10 percent by weight of an olefinic polymer; and from about 0.05 to about 5.0 percent by weight of the total propellant composition of chromium nitrate as a burning rate acceleration catalyst.
 15. A solid smokeless propellant composition consisting essentially of from about 45 to about 90 percent by weight of a solid inorganic oxidizing salt of ammonia; from about 55 to about 10 percent by weight of an olefinic polymer; and from about 0.05 to about 5.0 percent by weight of the total propellant composition of ferric nitrate hydrate as a burning rate acceleration catalyst.
 16. A solid smokeless propellant composition consisting essentially of from about 45 to about 90 percent by weight of a solid inorganic oxidizing salt of ammonia; from about 55 to about 10 percent by weight of asphalt; and from about 0.05 to about 5.0 percent by weight of the total propellant composition of chromium nitrate as a burning rate acceleration catalyst.
 17. A solid smokeless propellant composition consisting essentially of from about 45 to about 90 percent by weight of a solid inorganic oxidizing salt of ammonia; from about 55 to about 10 percent by weight of asphalt; and from about 0.05 to about 5.0 percent by weight of the total propellant composition of chromium nitrate as a burning rate acceleration catalyst. 